If the signs held no content not consistently upheld as free speech (threats, obscenity, etc..) they should not be held as a basis to force protesters to leave.
But that's not what's happening. Try standing by a presidential motorcade with any sign that expresses dissatisfaction with the president, his party or his policies. You will be told to move. And if you don't you will be arrested. Not for obscenity or making a threat, mind you. The charge will be "creating a disturbance" or "disorderly conduct".
And that is intolerable in a free country.
We had a presidential motorcade go by work after the mountain fires were delt with. All the hippy morons at my company went out with signs, nobody got told to move, nobody got arrested, and some of their signs actually were obscene. Sorry Freeeee but there isn't some universal thing, they aren't clearing out all protesters from all motorcade paths, I know the liberal journalists want you to think that, but they're lying to you.